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Substrate concentration

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

The rate of an enzyme-catalyzed reaction increases to a maximum rate, Vmax, with increasing substrate concentration. Vmax represents saturation of the enzyme with substrate. Km, the Michaelis constant, represents substrate concentration which produces half of Vmax. It is a measure of affinity of the enzyme for its substrate: the smaller Km, the greater is the affinity.

Practically, this means:

high concentrations of substrate should be used when testing in vitro activity of an enzyme
Vmax and Km values can be determined in vitro and in vivo to compare the contribution of a given enzyme to a specified metabolic reaction
a plot of the reciprocal of substrate concentration (x axis) against reciprocal of rate of reaction (y axis) can give Vmax - the reciprocal of the y-axis intercept - and Km - the negative reciprocal of the x-axis intercept. This is termed a Lineweaver-Burk plot.

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